WO 03/048034 describes a process in which, in a first stage, methane is reacted with steam in a first catalytic reactor to generate carbon monoxide and hydrogen (“synthesis gas”) in a so-called reforming stage, and, in a second stage, the resulting synthesis gas is subjected to a Fischer-Tropsch reaction in a second catalytic reactor to generate hydrocarbons of higher molecular weight and that are usually liquid at ambient temperatures. The overall result is to convert methane gas to liquid hydrocarbons, hence the conversion is sometimes referred to as gas-to-liquid (“GTL”).
The above-described conversion is of interest because it enables natural gas occurring at an oil or gas well to be converted into valuable and useful liquid hydrocarbons which are easier to transport.
WO 03/048034 discloses that the reforming stage is an endothermic reaction for which heat may be provided by combustion of methane over a palladium or platinum catalyst. However, methane does not catalytically combust in air until it reaches a temperature of about 400° C. Therefore, in order to start the reforming stage, means must be provided for raising the temperature of the combustion catalyst to about 400° C. or above before introducing methane or natural gas into the reforming reactor. Of the possibilities available, electrical heating may not be practicable on a commercial plant scale, and use of a duct burner in which there is direct contact between a flame and the gas to be heated would generate water which would condense on the cold catalyst and potentially cause damage. The invention overcomes the problem in a surprising and unexpected manner by employing oxygenates generated in the Fischer-Tropsch reaction stage of the conversion. Furthermore, the invention makes use of the oxygenates in the steady-state operation of the combustion process, i.e. after the reforming stage has satisfactorily started.